Pennellii LA716 Research Articles

Characterization of Solanum sp. Lycopersicon section for density and types of leaf trichomes and resistance to whitefly and tomato pinworm

Resistance genes to pests such as Bemisia tabaci and Tuta absoluta can be abundant in wild tomato genotypes. For breeding program initiatives, the characterization of the germplasm in terms of resistance to pests and related morphoanatomical characteristics is essential. Thus, the objective of this study was to evaluate the resistance of different accessions of species of Solanum sp., section Lycopersicon to B. tabaci and T. absoluta and establish a relationship with the types of trichomes present on the leaf surface. Whitefly oviposition, nymphs, and exuviae were investigated in 35 genotypes. On the leaf surface of the genotypes, glandular and non-glandular trichomes were identified and quantified. Based on the results, the genotypes were chosen for pinworm testing. Thirteen tomato genotypes were investigated, including Solanum lycopersicum var. cerasiforme, two accessions of S. lycopersicum, and ten wild accessions of Solanum sp., section Lycopersicon. At 7, 14, 21, and 28 days after infestation, eggs were counted on the abaxial surface of the leaflets, and the extent of damage caused by the tomato leafminer was determined using multivariate analysis and the area under the attack severity progress curve. Leaf trichomes of the 13 pre-selected genotypes were identified and quantified. The findings for the whitefly showed that wild genotypes were more resistant than the commercial ones due to the presence of trichomes, mainly glandular trichomes. According to principal component analysis, stronger materials in whitefly tests correlated more with the number of glandular trichomes. Finally, glandular trichomes positively correlate with the genotype's defense against pests. Solanum pennellii LA-716 and S. habrochaites var. hirsutum PI-127826 were the genotypes with the lowest number of oviposition and damage caused by the moth. This trait was also related to the higher density of glandular trichomes. The results show variability among accessions of the same species for trichome density and pest resistance. This information allows the choice of the best accessions among the species when defining the parents to be used in initial crosses of breeding programs.

Relationship between Acylsugars and Leaf Trichomes: Mediators of Pest Resistance in Tomato.

Simple SummarySeveral pests have the potential to cause major damage to tomatoes. The two-spotted spider mite and whitefly are examples of pests that attack tomato crops. Management of these pests involves several techniques; the use of chemical products is the most adopted strategy. However, growing resistant genotypes is a promising strategy in pest management, reducing the use of chemical products. In this work, we sought to identify genotypes more resistant to the mite and whitefly using advanced populations of tomato (F2BC3) obtained from the cross between S. lycopersicum “Redenção” and S. pennellii, accession LA-716. Results indicated a greater resistance in the genotypes with high levels of acylsugars, a chemical compound commonly found in S. pennellii tomatoes. Consequently, genotypes with increased levels of acylsugar can be used in breeding programs for pest resistance.Tomato plants are highly susceptible to pests. Among the control methods, genetic improvement with introgression of resistance genes from wild accessions into commercial tomato lines is the best alternative for an integrated pest management (IPM). Thus, the objective of this study was to select tomato genotypes in advanced populations (F2BC3), with higher levels of acylsugar content, greater recurrent parent genome recovery, and resistance to Tetranychus urticae and Bemisia tabaci inherited from Solanum pennellii. For pest resistance, bioassays were assessed: nine high-acylsugar genotypes, four low-acylsugar genotypes, and the parents, Solanum lycopersicum or ‘Redenção’, and Solanum pennellii LA-716. Glandular and non-glandular trichomes were quantified. A negative correlation was measured between acylsugar content in the leaflets and pest behavior. Pest resistance was found in the selected F2BC3 genotypes with high-acylsugar content, indicating that this allelochemical was efficient in controlling the arthropod pests.

Acylsugars in tomato varieties confer resistance to the whitefly and reduce the spread of fumagine

ABSTRACT Whiteflies (Bemisia tabaci) are a serious threat to tomato (Solanum lycopersicum) yield and production since all varieties are highly susceptible to this insect. The wild tomato Solanum pennellii shows resistance towards whiteflies infestation due the high contents of acylsugars presents in its leaflets, which is not observed in S. lycopersicum. Thus, plants from the F2BC2 population derived from the cross between the cultivar S. lycopersicum ‘Redencao’ and S. pennellii (accession LA-716) were selected for acylsugars levels and evaluated for resistance to whitefly and fumagine, a saprophyte fungus from genus Capnodium (sooty mold) that grows on leaves using whiteflies excretion. Biological behavior of B. tabaci was significantly influenced by the levels of acylsugars on the leaflets of the different genotypes. Solanum pennellii and the genotypes with higher acylsugars contents exhibited the lowest whitefly oviposition preference, number of nymphs, exuviae and adult survival. Also, the percentage of leaf coverage with fumagine was significantly reduced on leaves of the S. pennellii and the genotypes with higher acylsugars. Thus, it confirms that the use of S. pennellii LA-716 enabled the introgression of genes to increase the degrees of resistance in the F2BC2 genotypes. Finally, the results presented suggest that the genotypes RVTA-2010-31-177pl#39, RVTA-2010-31-319pl#214 and RVTA-2010-83-347pl#257 can be used as potential sources of genes for resistance to B. tabaci in tomato breeding programs.

<p class="Body"><strong>Impact of leaflet trichomes on settlement and oviposition of <em>Tetranychus evansi </em>(Acari: Tetranychidae) in African and South American tomatoes</strong></p>

Red spider mite (Tetranychus evansi) is considered one of the main tomato pests in Africa. As an alternative to chemical control, the use of pest-resistant cultivars has been considered a desirable and environment-friendly choice. Therefore, our study aimed to evaluate the influence of trichomes on settlement and oviposition preferences of T. evansi in African tomato varieties, besides comparing them to South American wild tomato species. First, free- and no-choice laboratory tests were carried out to investigate settlement and oviposition preferences of females on leaflets of two South American wild tomato species (Solanum pennellii LA-716 and S. habrochaites var. hirsutum PI134417) and five African tomato varieties (S. lycopersicum cv. Kekefo, Akikon, TLCV15, Tounvi, and TOML4), the latter are widely grown in Benin. Thereafter, leaf trichome types were determined and densities were estimated and then correlated to numbers of settled females and laid eggs on leaflets of each assessed genotype. According to our findings, females strongly preferred to settle and oviposit on African varieties rather than on South American genotypes. Regarding trichome density, non-glandular type Va showed significant positive correlations with both studied parameters, with the highest amounts in African genotypes. Conversely, glandular trichome density (mainly types I, IV, and VI) presented significant negative correlations with preference indicators, with the largest densities in South American species. The high density of non-glandular trichomes on leaflets of the varieties Akikon, Tounvi, Kekefo, TOML4, and TLCV15 might have been one of the causes of preference of T. evansi females.

Base temperature for node emission and plastochron determination in tomato species and their hybrids

Abstract: The objective of this work was to estimate the base temperature for node emission and plastochron determination in wild species of tomato, in the Redenção cultivar, and in their respective interspecific F1 hybrids. The wild accessions Solanum pimpinellifolium AF 26970, Solanum galapagense LA-1401, Solanum peruvianum AF 19684, Solanum habrochaites var. hirsutum PI-127826, Solanum habrochaites var. glabratum PI-134417, and Solanum pennellii LA-716; the cultivar Redenção (Solanum lycopersicum); and their respective interspecific hybrids were evaluated, on the transplanting dates 12/22/2015, 2/12/2016, and 4/6/2016. The base temperature was estimated using the least mean squared error of the linear regression between the number of nodes and the accumulated thermal sum. The plastochron for the main stem and the first three lateral stems was estimated using the base temperature. The base temperature for node emission and plastochron determination varied from 4.5 to 14.8°C. The species S. habrochaites var. hirsutum accession PI-127826, S. habrochaites var. glabratum accession PI-134417, and their hybrids with the Redenção cultivar showed the lowest base temperatures and plastochron for the main stem, whereas the remaining wild species and interspecific hybrids had a base temperature near that of cultivated tomato. Wild species and interspecific hybrids of tomato show a great variation in base temperature for node emission and plastochron determination.

Combination of Acylglucose QTL reveals additive and epistatic genetic interactions and impacts insect oviposition and virus infection

Acylsugars are important insect defense compounds produced at high levels by glandular trichomes of the wild tomato, Solanum pennellii. Marker-assisted selection was used to select for plants containing the three AGQTL named AG3QTL, AG4QTL, and AG11QTL from self-pollinated populations derived from an interspecific backcross population of CU071026 x (CU071026 x S. pennellii LA716). High acylglucose-accumulating lines were selected from these populations that possess these three AGQTL and the fewest number of extraneous S. pennellii LA716 introgressions. Incorporation of these three acylglucose QTL in the presence of the five standard S. pennellii introgressions of CU071026 altered acylsugar level and sugar moiety, demonstrating epistatic interactions between the acylglucose QTL on both of these traits. Comparison of the lines generated from the two breeding techniques indicated the three acylglucose QTL are essential but not necessarily sufficient for the production of elevated levels of acylglucose acylsugars. Fine-mapping of AG3QTL, AG4QTL, and AG11QTL resulted in less than 1 Mbp intervals for the locations of AG4QTL and AG11QTL; proposals of the causal genes underlying these acylglucose QTL are discussed. Characterization of the fatty acid profile of lines selected out of the interspecific backcross populations revealed an increase in the proportion of acylsugar n-C10 fatty acid acyl chains, possibly governed by one or more of the three acylglucose QTL. Characterization of the acylsugar profile of acylglucose lines selected from the interspecific backcross populations also demonstrated interactions among the acylglucose QTL to further modulate the diversity of acylsugars accumulated. Evaluation of an acylglucose line and controls against the tomato insect pest Frankliniella occidentalis demonstrated that levels of resistance differed among these lines and that the acylsugars accumulated by the acylglucose line were effective at reducing both F. occidentalis oviposition and incidence of Tomato spotted wilt orthotospovirus. However, of some of the acylglucose lines and hybrids tested against Spodoptera exigua did not indicate differences for larval weight gain and survival.

De Novo Assembly of a New Solanum pennellii Accession Using Nanopore Sequencing.

Updates in nanopore technology have made it possible to obtain gigabases of sequence data. Prior to this, nanopore sequencing technology was mainly used to analyze microbial samples. Here, we describe the generation of a comprehensive nanopore sequencing data set with a median read length of 11,979 bp for a self-compatible accession of the wild tomato species Solanum pennellii We describe the assembly of its genome to a contig N50 of 2.5 MB. The assembly pipeline comprised initial read correction with Canu and assembly with SMARTdenovo. The resulting raw nanopore-based de novo genome is structurally highly similar to that of the reference S. pennellii LA716 accession but has a high error rate and was rich in homopolymer deletions. After polishing the assembly with Illumina reads, we obtained an error rate of <0.02% when assessed versus the same Illumina data. We obtained a gene completeness of 96.53%, slightly surpassing that of the reference S. pennellii Taken together, our data indicate that such long read sequencing data can be used to affordably sequence and assemble gigabase-sized plant genomes.

Combination of QTL affecting acylsugar chemistry reveals additive and epistatic genetic interactions to increase acylsugar profile diversity

The tomato breeding line, CU071026, was bred to accumulate high levels of the insect control compounds called acylsugars, which are exuded from glandular trichomes. The acylsugars of CU071026 exhibit a characteristic profile of acylsugar composition and constituent fatty acid acyl groups that is distinct from that of the progenitor wild tomato, Solanum pennellii LA716. A prior study reported the transfer of three QTL (FA2, FA7, and FA8), from S. pennellii LA716, that are associated with changes in acylsugar chemistry into CU071026 and demonstrated that the resulting lines, each of which possesses one of these QTL, displayed a unique acylsugar and fatty acid profile distinct from that characteristic of the acylsugars of CU071026 and each other. The current study utilized marker-assisted backcrossing to combine pairs of two of these QTL or all three of these QTL. This created a new set of lines, which allowed evaluation of the combinatory effects of FA2QTL, FA7QTL, and FA8QTL, on acylsugar level and acylsugar and fatty acid profile and diversity. Analysis of the new tomato lines revealed that these QTL interacted additively and epistatically to alter acylsugar level and chemistry, increasing the diversity of fatty acid constituents and/or acylsugar chemotypes present in the exudates of some of the lines. Extensive characterization of the lines for acylsugar level, through a spectrophotometric invertase assay, and acylsugar chemistry, through gas and liquid chromatography-mass spectrometry, allowed association of the QTL interactions with aspects of acylsugar chemotype. The evaluated fatty acids and acylsugars accumulated by the set of lines generally displayed high heritability and minimal environmental effect, which is discussed. The QTL interactions that govern a more diverse acylsugar and fatty acid profile provide valuable information for the generation of tomato lines with improved acylsugar efficacy against pests of tomato.

Repellent effects of various cherry tomato accessions on the two-spotted spider mite Tetranychus urticae Koch (Acari: Tetranychidae).

Several studies have been conducted on resistance sources to improve the genetic resistance of farm-grown tomatoes to arthropod pests, including phytophagous mites. In the present study, we evaluate the behavior of the two-spotted spider mite on different cherry tomato accessions to identify possible sources of resistance (repellent effect) to this pest. Sixty-four accessions of cherry tomatoes, Solanum lycopersicum var. cerasiforme (Dunal), were tested. In addition, a commercial cultivar of cherry tomato cv. Sweet Grape (susceptible pattern) and the wild tomato accession Solanum pennellii Correll LA-716 (multiple pest resistance) were evaluated as well. The distance traveled by mites on the leaflet surface over time varied largely among cherry tomato accessions. The wild genotype, S. pennellii LA-716, showed the smallest traveled distance on the leaflet surface (0.8 to 1.1 mm over time), and the variety cv. Sweet Grape was one of the genotypes with highest traveled distance (16.2 to 16.4 mm over time). The cherry tomato accessions 2298-42, RVTC-03, and 6889-53 showed a decrease in the traveled distance by mites over time, similar to that as observed in the wild tomato accession LA716. These accessions showed mite repellence levels similar to those of the wild genotype and may, therefore, be good candidates for breeding programs dealing with resistance to mites.

Quantitative trait loci regulating the fatty acid profile of acylsugars in tomato

Acylsugars are secondary metabolites with proven insect resistance properties that are produced by many Solanaceous species including Solanum pennellii, a wild relative of tomato. The acylsugar chemotypes of S. pennellii varies greatly within its natural range and might be the product of plant/insect coevolution. The S. pennellii accession LA716 was used to transfer increased levels of acylsugar production into the cultivated tomato, resulting in the acylsugar tomato breeding line CU071026. S. pennellii accession LA716 produces high levels of acylsugars with chemotypes that differ greatly from those produced by CU071026 or the trace acylsugars of cultivated tomato. Understanding the genetic regulation of acylsugar chemistry will aid efforts to breed acylsugar production into cultivated tomato, allowing for alteration of both acylsugar base moieties and fatty acid profiles. This study uses a BC1F1 population produced from the cross of S. pennellii LA716 and CU071026 with CU071026 as the recurrent parent to identify QTL that change the fatty acid profile of acylsugars. Multiple QTL and epistatic interactions between QTL were detected including three QTL on chromosomes 2, 5, and 7, which significantly alter the percentage of extended iso-odd branched fatty acids and straight chain fatty acids on the acylsugars. We also report the introgression of one of these QTL, FA 2, into CU071026, resulting in a new tomato line with significantly increased i11:0 as a percentage of the fatty acids in its acylsugars. Candidate genes for these QTL and the impacts of altering acylsugar fatty acid are discussed.

Quantitative trait loci regulating sugar moiety of acylsugars in tomato

Acylsugars are broad-spectrum insect resistance sugar esters produced at very high levels by some accessions of the wild tomato, Solanum pennellii. Transferring acylsugar production from S. pennellii LA716 to cultivated tomato through traditional breeding developed the benchmark acylsugar breeding line CU071026. The base moiety of acylsugars (sucrose vs. glucose) can vary among S. pennellii accessions. Additionally the accession S. pennellii LA716 produces almost exclusively acylglucoses, but the breeding line CU071026 derived from S. pennellii LA716 produces exclusively acylsucroses. This study uses a BC1F1 and a BC1F2 population derived from the cross CU071026 × (CU071026 × S. pennellii LA716) to identify and confirm the action of three quantitative trait loci (QTL) on chromosomes 3, 4, and 11. The QTL on chromosomes 3 and 11 are both required for acylglucose production, while addition of the chromosome 4 QTL affects the level of acylglucose produced in the presence of the QTL on chromosomes 3 and 11. A three-way interaction between these acylglucose QTL was confirmed with a post hoc ANOVA. Identification of these three QTL provides a blueprint for breeding to shift acylsucrose production to acylglucose production in tomato breeding lines. The implications of these QTL and two additional QTL affecting total acylsugar level in the BC1F2 are discussed.

Fine genetic mapping of RXopJ4, a bacterial spot disease resistance locus from Solanum pennellii LA716

The RXopJ4 resistance locus from the wild accession Solanum pennellii (Sp) LA716 confers resistance to bacterial spot disease of tomato (S. lycopersicum, Sl) caused by Xanthomonas perforans (Xp). RXopJ4 resistance depends on recognition of the pathogen type III effector protein XopJ4. We used a collection of Sp introgression lines (ILs) to narrow the RXopJ4 locus to a 4.2-Mb segment on the long arm of chromosome 6, encompassed by the ILs 6-2 and 6-2-2. We then adapted or developed a collection of 14 molecular markers to map on a segregating F(2) population from a cross between the susceptible parent Sl FL8000 and the resistant parent RXopJ4 8000 OC(7). In the F(2) population, a 190-kb segment between the markers J350 and J352 cosegregated with resistance. This fine mapping will enable both the identification of candidate genes and the detection of resistant plants using cosegregating markers. The RXopJ4 resistance gene(s), in combination with other recently characterized genes and a quantitative trait locus (QTL) for bacterial spot disease resistance, will likely be an effective tool for the development of durable resistance in cultivated tomato.

Quantitative trait loci increasing acylsugars in tomato breeding lines and their impacts on silverleaf whiteflies

Solanum pennellii LA716, a wild relative of tomato, produces acylsugars, an insect resistance compound with activity against many tomato insect pests. Breeding of cultivated tomato using S. pennellii LA716 as a donor parent has led to the development of the elite acylsugar-producing tomato breeding line CU071026. CU071026 contains five introgressed S. pennellii genomic regions, and produces acylsugars at moderate levels that are effective against insect pests. A BC1F1 population was created by crossing the F1 CU071026 × S. pennellii LA716 with CU071026 as the recurrent parent; this BC1F1 population was used to identify additional regions of the S. pennellii genome important for further improvement of acylsugar production. This population was genotyped with 94 markers in the segregating regions and phenotyped for level of acylsugar production. Using QTLNetwork 2.1 for the detection of quantitative trait loci (QTL) and epistatic interactions, this study identified five QTL for total acylsugar level. Additionally, two epistatic interactions between QTL were found to control significant levels of total acylsugar production. Two of the QTL identified were further evaluated in silverleaf whitefly (Bemisia tabaci) field cage trials using acylsugar breeding lines that differ for the presence/absence of these QTL. While high levels of silverleaf whitefly resistance were observed in all acylsugar breeding lines, lines containing the additional QTL on either chromosomes 6 or 10 had increased levels of total acylsugar production and reduced incidence of whitefly. Acylsugar lines containing the chromosome 6 QTL also had increased density of the type IV glandular trichomes which produce and exude acylsugars.

Seedling salt tolerance in tomato

Soils with higher concentrations of salt are becoming more and more a constraint for many crops to obtain high yields. Wild tomato species, adapted to adverse environments, are a potential reservoir for genes underlying quantitative trait loci (QTL) related to salt tolerance in tomato. In this study two introgression line (IL) libraries derived from two different wild species, Solanum pennellii LA716 and Solanum lycopersicoides LA2951, were used to identify QTLs for salt tolerance in the seedling stage. In the S. pennellii IL library, four major QTLs were identified on chromosomes 6, 7 and 11. In the S. lycopersicoides IL library, six major QTLs were discovered which are located on chromosomes 4, 6, 9 and 12. Co-localization of QTLs on chromosome 6 in the two IL libraries and previously reports hinted that this locus might be conserved in the tomato crop. Three S. pennellii ILs (IL6-2, IL7-1 and IL7-5) harboring QTLs on chromosome 6 and 7 were crossed. Semi-dominance and dominance were shown for these three QTLs, and non-additive and epistatic interactions between them were observed.

Salt tolerance in Solanum pennellii: antioxidant response and related QTL

BackgroundExcessive soil salinity is an important problem for agriculture, however, salt tolerance is a complex trait that is not easily bred into plants. Exposure of cultivated tomato to salt stress has been reported to result in increased antioxidant content and activity. Salt tolerance of the related wild species, Solanum pennellii, has also been associated with similar changes in antioxidants. In this work, S. lycopersicum M82, S. pennellii LA716 and a S. pennellii introgression line (IL) population were evaluated for growth and their levels of antioxidant activity (total water-soluble antioxidant activity), major antioxidant compounds (phenolic and flavonoid contents) and antioxidant enzyme activities (superoxide dismutase, catalase, ascorbate peroxidase and peroxidase) under both control and salt stress (150 mM NaCl) conditions. These data were then used to identify quantitative trait loci (QTL) responsible for controlling the antioxidant parameters under both stress and nonstress conditions.ResultsUnder control conditions, cultivated tomato had higher levels of all antioxidants (except superoxide dismutase) than S. pennellii. However, under salt stress, the wild species showed greater induction of all antioxidants except peroxidase. The ILs showed diverse responses to salinity and proved very useful for the identification of QTL. Thus, 125 loci for antioxidant content under control and salt conditions were detected. Eleven of the total antioxidant activity and phenolic content QTL matched loci identified in an independent study using the same population, thereby reinforcing the validity of the loci. In addition, the growth responses of the ILs were evaluated to identify lines with favorable growth and antioxidant profiles.ConclusionsPlants have a complex antioxidant response when placed under salt stress. Some loci control antioxidant content under all conditions while others are responsible for antioxidant content only under saline or nonsaline conditions. The localization of QTL for these traits and the identification of lines with specific antioxidant and growth responses may be useful for breeding potentially salt tolerant tomato cultivars having higher antioxidant levels under nonstress and salt stress conditions.

Resistance of tomato genotypes to the silverleaf whitefly mediated by acylsugars

Acylsugars in the leaflets of the wild accession LA-716 (Lycopersicon pennellii) gives resistance to Bemisia spp., which causes expressive losses to the tomato crop. The goal of this work was to evaluate the resistance to the silverleaf whitefly (Bemisia tabaci biotype B) of previously selected genotypes, based on the level of acylsugars in the leaflets. F2BC1 plants {F2[Lycopersicon esculentum TOM 584 x (L. esculentum TOM 584 x L. pennellii LA-716)]} were selected for extreme contents of acylsugars: BPX-370B pl#30-275, BPX-370B pl#79-278, BPX-370B pl#30-380, BPX-370B pl#25-271 (high contents), BPX-370B pl#30-02, BPX-370B pl#30-142 (low contents). These genotypes, along with the parents TOM 584 and LA-716, were submitted to a silverleaf whitefly infestation. Oviposition and nymph development were evaluated. The oviposition on the genotypes BPX-370B pl#30-275 and BPX-370B pl#30-380 was significantly lower to that which occurred on the genotype TOM 584 and in the other genotypes of the F2RC1 generation. The four genotypes selected for high acylsugar contents presented the lowest number of nymphs, except to LA-716. Although the number of eggs in the BPX-370B pl#25-271 and BPX-370B pl#79-278 genotypes (high contents) was elevated, the number of nymphs was reduced, similarly to the other high-acylsugar genotypes, probably due to antibioses effect.

The role of specific tomato volatiles in tomato-whitefly interaction.

Bemisia tabaci (whitefly) infestations and the subsequent transfer of viruses are the cause of severe losses in crop production and horticultural practice. To improve biological control of B. tabaci, we investigated repellent properties of plant-produced semiochemicals. The mix of headspace volatiles, collected from naturally repellent wild tomato accessions, influenced B. tabaci initial choice behavior, indicating a role for plant semiochemicals in locating host plants. A collection of wild tomato accessions and introgression lines (Solanum pennellii LA716 x Solanum lycopersicum 'Moneyberg') were extensively screened for attractiveness to B. tabaci, and their headspace profiles were determined by means of gas chromatography-mass spectrometry. Correlation analysis revealed that several terpenoids were putatively involved in tomato-whitefly interactions. Several of these candidate compounds conferred repellence to otherwise attractive tomato plants when applied to the plant's branches on paper cards. The sesquiterpenes zingiberene and curcumene and the monoterpenes p-cymene, alpha-terpinene, and alpha-phellandrene had the strongest effects in free-choice bioassays. These terpenes also elicited a response of receptors on the insect's antennae as determined by electroantennography. Conversely, the monoterpene beta-myrcene showed no activity in both assays. B. tabaci apparently uses, besides visual cues, specific plant volatile cues for the initial selection of a host. Altering whitefly choice behavior by manipulation of the terpenoid composition of the host headspace may therefore be feasible.

Resistance of tomato genotypes with high level of acylsugars to Tetranychus evansi Baker &amp; Pritchard

The Lycopersicon pennellii accession LA716 has been used as a source of arthropod pest resistance in tomato breeding programs due the high contents of acylsugars presents in its leaflets. We investigated the relationship between high foliar acylsugar contents and repellence to spider mite Tetranychus evansi in plants with contrasting acylsugar levels, selected from F2 and BC1F2 (= F2 of the first backcross towards L. esculentum) generations derived from the interespecific cross L. esculentum 'TOM-584' &lt;FONT FACE=Symbol&gt;´&lt;/FONT&gt; L. pennellii LA716. Mite resistance was assessed by a repellence test. Plants selected for high levels of acylsugars in leaflets had mite repellence levels similar to that of LA716. The high correlation confirmed the association between high acylsugar levels and mite repellence.

Development of PCR-based markers from the tomato glutamate oxaloacetate transaminase isozyme gene family as a means of revitalising old isozyme markers and recruiting new ones

Sequences annotated as aspartate aminotransferases (synonymous with glutamate oxaloacetate transaminases) in the SOL Genomics Network unigene database were used to design 10 pairs of PCR primers for genetic marker development. These primer pairs generated nine CAPS markers, two SCAR markers and one SSR marker, which were bin-mapped using a set of tomato introgression lines (IL) derived from Lycopersicon esculentum cv. M82 and Lycopersicon pennellii LA716. Based on their bin locations, these markers are largely dispersed throughout the tomato genome and appear to have tagged all four of the glutamate oxaloacetate transaminase (Got) isozyme marker genes placed on the classical genetic map of tomato. Orthologous relationships with Arabidopsis aspartate aminotransferase (Asp) genes suggest the existence of at least two additional functional Got genes in tomato that have also been tagged by these markers and likewise an additional functional Asp gene in Arabidopsis. The Got-2 isozyme marker has often been used for the marker-assisted breeding of the I-3 gene for Fusarium wilt resistance introgressed from L. pennellii LA716. The Got-2 CAPS marker that we have developed offers a facile PCR-based alternative to the isozyme marker for the marker-assisted breeding of I-3. However, all of the PCR-based markers we have developed have the potential to assist the breeding of linked traits introgressed from wild relatives of tomato.

Amplified Fragment Length Polymorphism Mapping of Tomato Backcross Populations

Tomato backcross populations of Lycopersicon exculentum cv. Money Maker x Lycopersicon pennellii LA716 were used for construction of an Amplified Fragment Length Polymorphism (AELP) map based on pennellii markers. Ten primer combinations (7 of Eco-Mse and 3 of Pst-Mse) were used. This map spanned 893.7 cM and contained 187 AFLP markers, consisting 130 previously found markers and 57 new markers. A total of 141 markers were found from Eco-Mse primer combination and 46 from Pst-Mse primer combination. The Eco-Mse AFLP markers were not evenly distributed over the chromosomes. The Pst-Mse AFLP markers were found quite frequently and evenly distributed in the more distal part of the chromosomes. Eco-Mse markers were found quite more in numbers in chromosomes 5 and 9, whereas Pst-Mse markers in chromosomes 1 and 7. In chromosomes 4, 6, 7 and 8, the new markers and previously found markers were found quite equal in numbers. The average number of informative markers per primer combination was 18.7 ranging from 6 (E33M47) to 36(E35M48). The average size of map per chromosome was found 74.5 cM ranging from 46.2 cM of chromosome 8 and 105.5 cm of chromosome 3. Fourteen BC1 plants for BC2 and subsequently 12 BC2 plants for BC3 generation were selected to obtain inbred lines with genes of interest. BC1 plants were selected each representing about 50% Lycopersicon pennellii LA716 genome and BC2 plants were selected each representing about 25% genome coverage, and together cover 100% of the Lycopersicon pennellii genome based on scored markers J. Inst. Agric. Anim. Sci. 2003 24:21-28.